The present invention relates to an apparatus for multiplexing between on-board units of a vehicle by using wire harnesses.
Recently, various controls in a vehicle are performed by an on-board computer and the associated electrically controlled equipments. Thus, large amounts of electric wiring are used in the vehicle. Those electric wiring such as the wire harnesses have the potential for causing short-circuit. Therefor, various apparatus for detecting the short-circuit of wire harnesses for power supply are proposed in the past.
One of them is disclosed in Japanese Patent publication No. 4-17809 (1992), in which the rated consumption currents for respective loads are calculated in advance, the occurrence of a normality due to the short-circuit is detected by comparing sum of the rated consumption currents with sum of the current one in the vehicle.
However, when a wire harness is installed into a vehicle body, the harness may be jammed into the vehicle body and/or the coating of the harness may be broken due to the rubbing of the harness on metal portions of the vehicle body. Therefore, a core wire of an electric power source may short to an ground portion of the vehicle body, and thus serious accidents such as the fire of the vehicle may break out in the worst case.
In the above prior art, it is constructed such that the serious accidents can be prevented immediately by cutting off the whole current. Therefore, when such the accidents occurs during driving, a power source is cut off. As a result, the vehicle stops suddenly. Further, when the driver changes the load of an electric system, it is required to change the predetermined rated values Therefore, there was a possibility that a malfunction occurs. In addition, while the short-circuit of the wire harness can be detected, the processing after the detection of the short-circuit can not be performed.